Structural, optical, and magnetic properties of Co-doped ZnO nanorods fabricated by a facile solution route

In this study, a facile two-step solution route is demonstrated for the fabrication of Co-doped ZnO nanorods with diverse doping levels. The combination of XRD, EDS, and XPS measurements reveals that Co ions are successfully incorporated into the ZnO matrix and exist in the host lattice under the 2+ valence state. The substitution of Co2+ for Zn2+ does not change the wurtzite structure of ZnO nanocrystals. Co2+ dopant inhibits the dissolution of the intermediate product, thus, allowing a relatively slow and uniform deposition of the effective ions on the growing tiny rods. As a consequence, the obtained ZnO nanorods become longer and thinner with the increase in dopant concentration. Homogeneous substitutional doping is further verified by UV–vis absorption and photoluminescence spectroscopy. An obvious redshift in the wavelength of the absorption edge is observed in the doped ZnO samples, which can be attributed to the sp–d exchange interactions between the electrons in the conduction band of ZnO and the localized d electrons of the Co2+ cations. A remarkable quenching of yellow-green luminescence that results from doping is explained by an energy transfer mechanism. Furthermore, the doped ZnO exhibits room-temperature ferromagnetism, which is greatly suppressed and replaced by paramagnetism at higher doping levels.